Civil Engineering Reference
In-Depth Information
Other types of cracking
For more detailed work on non-structural cracks in concrete, see Concrete
Society Technical Report No. 22 'Non-Structural Cracks in Concrete'
(Concrete Society, 2010).
1.4 NDT and laboratory methods
Any investigation can conveniently be split into two stages:
Stage 1:
An initial survey to identify the cause of the problems.
Stage 2:
An extension of the stage 1 survey, perhaps using a limited number
of techniques to identify the extent of the defects revealed by stage 1.
The advantages of such an approach are clear. In the stage 1 survey, work
can be carried out on selected areas showing typical defects but choosing
these, as far as possible, from areas with simple access, i.e. ground level,
roof level, from balconies, etc. Occasionally, a lightweight scaffold tower
or an electrically powered hydraulic lift can be used to advantage. One or
more areas apparently free from defect would also be examined in this initial
survey as it is frequently found that, by comparing good areas with bad,
the reason for the problems emerges by simple comparison. An excellent
approach to stage 1 is to view the structure after heavy rain and to identify
the weakest details from the design drawings. Where water sheds and where
the weakest details are should most certainly be included in this initial survey.
In stage 2, once the defects have been identified, it is often necessary to
quantify the extent of the problems. This may be as simple as carrying out
a covermeter survey over the whole structure, where low cover has been
identified as the problem, to the application of one or more of the other
techniques described below.
1.4.1 Visual survey
After collecting as much background data as possible, any testing regime
should begin with a thorough visual survey of the structure. This may
conveniently be recorded on a developed elevation giving particular attention
to the following defects:
• Cracks or crazing
• Spalling
• Corrosion of steel and rust staining
• Hollow surfaces
•
Honeycombing due to poor compaction or grout loss
•
Varying colour or texture
•
Areas in which remedial finishing work had already been carried out
•
External contamination or surface deposits
•
Wet or damp surfaces.
